How to get all services that are tagged with a specific tag in *.services.yml?

Question

Is there an easy (supported) way to programatically get all services in Drupal 8 that are tagged with a specific tag?

For example getting all services that are tagged with "breadcrumb_builder" tag

Example for a service tag from book module:

services:
  book.breadcrumb:
    class: Drupal\book\BookBreadcrumbBuilder
    arguments: ['@entity_type.manager', '@current_user']
    tags:
      - { name: breadcrumb_builder, priority: 701 }

Now if i want to get all services from all (enabled) *.services.yml files that are tagged with "breadcrumb_builder"?

I have seen and read this: https://symfony.com/doc/3.4/service_container/tags.html

But this seems to be really hard work and I am not sure if its even possible that way without touching Drupal core.

The Reference Tagged Services method looked very promising at first, but seems not to be supported from Drupal by default.

Answer 1

You need to implement a service collector to collect your tagged services there is a good explanation about this in the Collecting Services Drupal documentation

Take a look at this example:

# core.services.yml:
string_translation:
  class: Drupal\Core\StringTranslation\TranslationManager
  arguments: ['@language.default']
  tags:
    - { name: service_collector, tag: string_translator, call: addTranslator }

The service definition has a tag whose name is service_collector, which is how to tell Drupal that a service is a service collector. The tag attribute on the tag definition tells what tag name the collected services need to be tagged with in order to be collected; this can be omitted to use the collecting service's ID as the tag name.

The call attribute on the tag tells Drupal that the TranslationManager::addTranslator() method should be called once for each collected service that is located.